This invention related to flame-retardant polymeric compositions, especially to thermoplastic compositions, particularly based on polyolefins, containing an intumescent flame-retardant system comprised substantially of a phosphorus component and an organic nitrogen component.
In U.S. Pat. No. 4,140,660 it has been suggested that phosphonic acid derivatives of isocyanuric acid are useful for imparting flame-retardant properties to polyurethanes. U.S. Pat. No. 4,001,177 also describes a combination of melamine and isocyanuric acid derivatives for imparting flame-retardant properties to polyamides.
U.S. Pat. No. 3,810,862 appears to be the first reference to disclose the use of an intumescent mixture to impart flame-retardant properties to polyolefins; this mixture consisting of ammonium polyphosphate, melamine and dipentaerythritol or melamine pyrophosphate and dipentaerythritol. In U.S. Pat. No. 4,312,805 (DE-OS 28 00 891), a three-component mixture of ammonium polyphosphate, melamine and polyamide 6 (of Example 6) is suggested, and in U.S. Pat. No. 4,198,493 (DE-OS 28 39 710) a further series of three-component mixtures are suggested consisting of ammonium polyphosphate, melamine and tris-(2-hydroxyethyl) isocyanurate (cf. Examples 2, 5, 6, 7, 8) or ammonium polyphosphate, pentaerythritol or tripentaerythritol and tris-(2-hydroxyethyl) isocyanurate (cf. Examples 4, 9) or ammonium polyphosphate, cyanuric acid and tris-(2-hydroxyethyl) isocyanurate (cf. Examples 13, 14) as intumescent agents imparting flame-retardant properties to polyolefins. It has also been disclosed (cf. U.S. Pat. No. 4,461,862) that a combination of ammonium polyphosphate and the reaction product of an oxygen acid of phosphorus with a hydroxy-alkyl derivative of isocyanuric acid can conveniently be used for this purpose.
U.S. Pat. No. 4,727,102, however, to Scarso discloses flame retardant polypropylene composition having a "V-O" UL 94 rating consisting of 15% ammonium polyphosphate and 20% of tris-(hydroxy-ethyl)-isocyanurate but the product had "poor mechanical and thermal characteristics." Scarso teaches to incorporate melamine cyanurate into the formulation in order to obtain a flame retardant polymer composition having good mechanical and thermal properties.
We have now found that a two-component system, consisting of ammonium polyphosphate (APP) and tris-(2-hydroxy-ethyl)-isocyanurate (THEIC) imparts very good flame-retardant properties to polyolefins. This was more particularly an unexpected result as the other components of the three- component systems specified hereinabove when used in a two-component system with ammonium polyphosphate did not have any flame-retardant activity whatsoever (cf. comparative Examples 1-12 herein) and the Scarso reference teaches that poor mechanical and thermal properties would be expected of this two component (APP-THEIC) system.
We have found that the two component flame retardant system of the invention provides:
(a) high flame retardancy properties; i.e. UL94-VO rating and high oxygen index; PA0 (b) high mechanical strength properties; PA0 (c) low smoke emission; and PA0 (d) improved environmental safety. PA0 a) a water-insoluble artificial, preferably cured, resin encapsulating the individual ammonium polyphosphate particles; PA0 b) a reaction product of a polyisocyanate with a carbodiimidization catalyst, the polycarbodiimide formed encapsulating the individual ammonium polyphosphate particles; PA0 c) a reaction product of a polyisocyanate and a polyhydroxy compound, the polyurethane formed encapsulating the individual ammonium polyphosphate particles; PA0 d) a reaction product of a polyisocyanate with a trimerization catalyst, the polyisocyanurate formed encapsulating the individual ammonium polyphosphate particles; PA0 e) a reaction product of a polyisocyanate and water, the polyurea formed encapsulating the individual ammonium polyphosphate particles; PA0 f) a cured melamine/formaldehyde-resin, the melamine/formaldehyde resin encapsulating the individual ammonium polyphosphate particles; PA0 g) a cured epoxide resin, the epoxide resin encapsulating the individual ammonium polyphosphate particles.